It would be difficult to overstate the complexity of the task a student teacher undertakes when she assumes responsibility for teaching her subject to a class during teaching practice. Vet, while issues surrounding teaching practice - such as the attitudes of trainees and their socialization - have frequently been studied (Zeichner, 1986a; Wragg,1982; Al-Hidabi, 1986), it is only recently that the actual classroom teaching of student teachers has attracted much sustained research attention (see, for example, Feiman-Nemser & Buchmann, 1986a, b, c; Leinhardt & Greeno, 1986; Bork & Livingstone, 1989). Consequently, little is known in detail about what students do, moment by moment, while engaging in the key practical component of their professional training. Considering that teaching practice - variously called the practicum, field experience, professional experience, teaching rounds, and so on - plays an essential part in all schemes of training (Collins, 1982), that training institutions in general have tended to increase the proportion of time devoted to school experience (Furlong, et al., 1988) and that students have frequently been found to view the practicum as the most valuable aspect of their course (Feiman-Nemser, 1983; Turney et al., 1985), the fact that the teaching of student teachers has been so little studied appears somewhat anomalous. This situation contrasts markedly with what is known about leaching in general from studies of experienced teachers. Research into the cognitive aspects of pedagogy has revealed something of the manifold complexities inherent in teaching. Thus the teacher may be viewed as a reflective professional who demonstrates 'knowledge-in- action' (Schon, 1983). Similar conceptions underlie perspectives which focus variously upon 'teacher decision making (Calderhead, 1980), 'teacher's craft knowledge' (McNamara & Desforges, 1978; Desforges & MacNamara,1979), or 'the knowledge base for teaching' (Shulman, 1986a, 1967). Drawing from such overlapping viewpoints, a composite picture of teaching emerges. Interacting with, say, thirty disparate individuals, who comprise the pupils in her care, the teacher engages in activities designed to illuminate her subject (Shulman, 1990). Her action is based on rapid and intricate discriminations among a multiplicity of overlapping events which often pass with bewildering speed (Doyle, 1986). She must simultaneously manage both the social order in the classroom and the development of academic work, and, where there is conflict between these twin goals, the former concern often seems to be accorded priority (Carter & Doyle, 1987). Thus the teacher's action seems designed to ensure that orderly states of activity are initiated and sustained (Brown & McIntyre,1989). An additional aspect of the teacher's action, which pervades the classroom, is the way she improvises pedagogical language, in an interactive setting, in an attempt to disclose subject matter knowledge (Erickson, 1982). The teacher also possesses an awareness of the differential abilities of pupils in the class and seeks to involve them in appropriate ways (Calderhead, 1980). Yet all her pedagogical action may be orchestrated into a seamless performance of such skill that its intricacy can easily be overlooked by an observer (McNamara, 1980). Thus it would appear that if teaching practice is conceived as an opportunity for learning through attempting to emulate what experienced teachers do, the student faces a central difficulty: much of the professional activity teachers engage in is not directly observable (Feiman-Nemser & Buchmann, 1986a, b, c). The student teacher may view the overt actions of a co-operating teacher, but she is not privy to the professional discriminations which inform these actions. Nor have teachers, in common with other professionals, been found to be naturally able to be explicit about their expertise in this regard (Berliner, 1986; McIntyre et el., 1988). And the student suffers still other disadvantages. Salient among these is the fact that she has to teach pupils she is barely acquainted with. Thus she does not possess the knowledge of the class, built up over many dozens of hours of interaction, that the co-operating teacher has, and so is likely to be hesitant in interpreting pupil behaviour. Nor does she have the store of knowledge, built up from years of exposure to other pupils and classes, that the experienced teacher may fall back on when she encounters a new class (Wragg & Wood, 1984). Similarly, while she may be enthused by her subject, she does not have the pedagogical knowledge of the subject matter that the experienced teacher will have accumulated (Shulman,1987). For instance, she is unlikely to know accurately what may be expected of pupils of different ages and abilities. Nor will she be keenly aware of the common misunderstandings that may need to be guarded against when she introduces pupils to a particular topic. Neither will she possess a store of useful analogies for explaining certain concepts, and so on (see, Shulman, 1986a, 1990; Wilson, et al. 1986).